Fluoroalkene-nucleophile adducts for analysis and removal of fluoroalkenes

ABSTRACT

A method for removing one or more fluorinated alkenes from a fluid comprises the step of contacting the fluid with an N-, S-, or P-containing nucleophile for a time sufficient to form an N-, S-, or P-containing nucleophile-fluoroalkene adduct. The nucleophile, and therefore the adduct, can be covalently bonded, coated or sorbed to a particulate support which can be enmeshed in a porous, fibrous web. In a preferred embodiment the fluorinated alkene can have the formula                    
     wherein A=F or R f ; X=H, F, Cl, R f , or YR f ; Z=H, F, Cl, or R f ; and Y=O, N, or S; with the proviso that at least one A=F, and at most one of Z and X is H; wherein each R f  is independently selected from the group consisting of highly fluorinated or perfluorinated alkyl groups; and a combination of any two R f  groups can be linked to form a cyclic structure. 
     The R f  alkyl chains may contain from 1-20 carbon atoms, with 1-12 carbon atoms preferred. The R f  alkyl chains may be straight, branched, or cyclic. Preferably, R f  is CF 3 , C 2 F 5 , or C 3 F 7 .

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 09/711,803filed Nov. 13, 2000, now pending, which is a continuation of U.S.application Ser. No. 09/154,350, filed Sep. 16, 1988, issued as U.S.Pat. No. 6,147,268.

FIELD OF THE INVENTION

This invention relates to fluoroalkene-nucleophile adduct formation forremoval, immobilization, or quantification of fluoroalkenes from fluids.

BACKGROUND OF THE INVENTION

Perfluoroalkane fluids have many industrial uses, such as coolants forelectronic devices (e.g., supercomputers) and as heat transfer media invapor-phase soldering processes. However, upon transient heating many ofthese perfluorinated liquids at high temperatures, toxic impurities mayform, such as certain fluoroalkenes, for example perfluoroisobutene(PFIB). These impurities may be hazardous to persons handling the liquidor operating equipment containing the contaminated liquid. Analyticalprocedures for the identification and quantification of the highlyvolatile low molecular weight fluorocarbons generally requirechromatographic separation and reference standards for calibration. Themore toxic perfluoroolefins such as PFIB are not readily available to beused as reference standards and transportation is a serious problem.Marhevka et al., Anal. Chem., 1982, 54, 2607-2610, describe a method togenerate a reference standard and suggest the use of an analyticalsurrogate, perfluorocyclopentene (PFCP), for calibration purposes.

Various methods have been suggested for reducing the hazard of PFIBexposure of operators of equipment that might inadvertently produce PFIB(Turbini, L. J., Zado, F. M., “Chemical and Environmental Aspects ofCondensation Reflow Soldering”, Electronic Packaging and Production,January, 1980, 49-59 and “Fluorinert Liquids”, 3M Publication No.98-0211-4411-2(78.2)R1 XY, June 1988). Some of these methods includetechniques of operating and maintaining vapor-phase soldering equipmentto avoid localized super-heating of perfluorinated liquids, thusreducing the amount of PFIB produced, and standards of designing workareas to provide sufficient ventilation to maintain PFIB levels at lessthan hazardous levels.

U.S. Defensive Publication T983,009 (June, 1979) describes a method ofconverting PFIB in a mixture of fluorine-containing compounds into arelatively nontoxic ether by contacting the mixture with a solution ofmethanol and a selected hydrogen halide. While this method does produceproducts which are generally less toxic than PFIB, it has disadvantages,including 1) being complex to perform in a continuous mode, sincevarious feed streams of reactants must be controlled, 2) using hazardoushydrogen halides (e.g., HF and HCl) as reactants, and 3) yieldingproducts which may create a disposal problem.

U.S. Pat. No. 3,696,156 describes a method of removing perfluoroolefinand perfluorochloroolefin impurities from saturated fluoroperhalocarboncompounds having two to six carbon atoms, by contacting the impurefluoroperhalocarbon in the vapor phase at about 180 to 250 degrees Cwith alumina containing a basic alkali metal or alkaline earth metalhydroxide or oxide.

U.S. Pat. No. 5,233,107 describes a process for removing olefinicimpurities from hydrogen-containing chlorofluorocarbons in the gas phaseat 200 to 400 degrees C over a zeolite. The contaminated higher boilingchlorofluorocarbons are preheated to convert the liquid to the gas phasein advance. The addition of 0.5 to 10% air or oxygen by volume to theprocess stream is recommended to keep coking at a very low level.

One of the disadvantages of processes utilizing elevated temperatures isthat they require handling hot gases contaminated with hazardouscompounds. In addition, certain fluorocarbons are unstable and generatea variety of olefinic and aliphatic impurities at elevated temperaturesespecially in the presence of catalytic surfaces.

Hall et al. Chemistry and Industry, March 6, 1989, 145-146, describeactivated carbon filters to provide protection against exposure to PFIBand note that some of the PFIB is hydrolysed to produce2H-perfluoroisobutyric acid and hydrogen fluoride. After storage andreuse of the exposed filter, 1,1,3,3,3-pentafluoropropene and1,1,1,3,3,3-hexafluoropropane were found in the effluent stream.

A system and method for purifying saturated fluoroperhalocarbon liquidsby removing olefinic impurities, such as PFIB, therefrom have beendisclosed in U.S. Pat. Nos. 5,300,714 and 5,507,941. Inorganic oxide,hydroxide, carbonate, or phosphate particles are used in the method.

England et al., J. Fluorine Chem. 1981, 17, 265-288, describe reactionsof amines with a dimer of hexafluoropropene and a perfluorovinyl sulfideprepared from hexafluoropropene. Anhydrous ammonia was added to asolution of hexafluoropropene dimer to form(1-amino-2,2,3,3,3-pentafluoropropylidene)propanedinitrile.

Coffman et al., J. Org. Chem., 1949, 14, 747-753, reported that ammoniareacted with tetrafluoroethylene forms an amine which splits out HF toform difluoroacetonitrile which then forms a trimer.

An organic amine-impregnated activated carbon composition, whichpreferably has been pre-treated, has been used in breathing gas filtersto enhance removal of various toxic perfluorocarbons as is disclosed inU.S. Pat. No. 5,462,908. There is no disclosure as to the composition ofthe treated material or the nature of the nucleophile used to form astable immobilized adduct with fluoroalkenes.

An exhaustive review of one of the fluoroalkenes is presented in “TheChemistry of Perfluoroisobutene,” by Y. V. Zeifman, et al., RussianChemical Reviews, 1984, 53 (March), 256-273. Reactions of PFIB withnumerous N, O, S, and P nucleophiles are discussed, without reference totheir quantitative analytical application or the ability of thesenucleophiles to react with other fluoroalkenes.

SUMMARY OF THE INVENTION

Briefly, this invention provides a method for removing one or morehighly fluorinated or perfluorinated alkenes (also referred tohereinbelow as a “fluoroalkene”) from a fluid, comprising the step ofcontacting the fluid with ammonium hydroxide or an organic nitrogen-,sulfur-, or phosphorus-containing nucleophile wherein the nucleophilicatom is N, S, or P (hereinafter sometimes referred to as N-, S-, orP-nucleophiles) for a time sufficient to form a nitrogen-, sulfur-, orphosphorus-containing nucleophile-fluoroalkene adduct. Preferably, theN-, S-, or P-nucleophile is sorbed on, or coated on, or bonded to, oritself can be, a support and can be used in a bed or cartridge. Morepreferably, the N-, S-, or P-nucleophile which can be sorbed on, orcoated on, or bonded to a support is enmeshed in or forms a fibrousmatrix, preferably a nonwoven matrix, which provides an essentiallyhomogeneous, porous material. Alternatively the N-, S-, or P-nucleophilecan be sorbed on, coated onto, or bonded directly to a porous matrix.Preferably, the nucleophile is ammonia or it comprises a nitrogen,sulfur or phosphorus nucleophile compound.

The optimum amount of nucleophile that can be loaded on a support varieswith the nature of the support. In general, it is preferred to load thenucleophile in an amount in the range of 0.1 to 10 weight percent, morepreferably 0.1 to 5 weight percent, based on the weight of the support.

In another aspect, the present invention provides a method forquantifying a highly fluorinated or perfluorinated alkene, for examplePFIB, comprising the steps of

a) providing a stable or unstable N-, S-, or P-containingnucleophile-fluoroalkene adduct, which may be sorbed to a support, and

b) quantifying for highly fluorinated or perfluorinated alkenes in afluid by either

1) measuring highly fluorinated or perfluorinated alkenes when the N-,S-, or P-containing nucleophile-fluoroalkene adduct is stable,displacing the adduct from the support when necessary, or

2) measuring the fluoride ion for indirect quantification of highlyfluorinated or perfluorinated alkenes, when the N-, S-, or P-containingnucleophile-fluoroalkene is unstable and produces fluoride ion.

In yet another aspect, the present invention describes a method forpreparing an adduct comprising the step of contacting an immobilized N-,S-, or P-containing nucleophile with a fluid comprising a fluoroalkenefor a time sufficient to form an N-, S-, or P-containingnucleophile-fluoroalkene adduct.

In still another aspect, the present invention provides a reactiveparticulate comprising an N-, S-, or P-containing nucleophile bonded orsorbed to a support which preferably has a high surface area. Thereactive particulate can react with a highly fluorinated orperfluorinated alkene to produce an N-, S-, or P-containingnucleophile-fluoroalkene adduct.

In a further aspect, the present invention provides N-, S-, or P-containing nucleophile-fluoroalkene adducts which have eliminated HF toform new nucleophile-substituted olefinic compounds and which can bemade to further react with other nucleophiles such as water or analcohol to form a new secondary adduct which undergoes further reactionsto form an amide or a vinyl ether when a nitrogen nucleophile was usedto prepare the initial nucleophile-fluoroalkene adduct.

In a still further aspect, there are provided stablefluoroalkene-nucleophile derivatives which can be used as analyticalstandards for quantification and identification of the more toxicfluoroalkene species, reducing the difficulties of manufacture andshipping hazardous material.

As used in this application:

“Adduct” means the addition product of a nucleophile and a fluoroalkenewith or without the elimination of a byproduct;

“fluid” refers to a material that is either a liquid or a gas at 25° C.and 760 mm Hg pressure, i.e., standard conditions;

“fluoroalkene” and “fluoroolefin” are used interchangeably;

“highly fluorinated alkene” means that more than half of the hydrogenatoms on the alkene have been replaced with fluorine atoms. It ispreferred that the carbon atoms immediately adjacent to the unsaturatedcarbon-carbon bond of “highly fluorinated alkenes” will have more thanhalf the total number of hydrogen atoms directly bonded to them replacedwith fluorine atoms, and most preferably the highly fluorinated alkeneis a perfluorinated alkene;

“highly fluorinated alkyl group” will have more than half the totalnumber of hydrogen atoms replaced with fluorine atoms. Although hydrogenatoms may remain, it is preferred that all hydrogen atoms be replacedwith fluorine to form a perfluoroalkyl group;

“stable” means that the fluoroalkene-nucleophile adduct can survive thethermal stress it is subjected to when injected into a gaschromatographic column at elevated temperatures needed to elute,identify, and quantify the compounds of interest; and

“nitrogen-, sulfur-, or phosphorus-nucleophile” (“N-, S-, orP-nucleophile”) means any nucleophile comprising one or more ofnitrogen, sulfur, or phosphorus as the nucleophilic site, and includesammonia and any organic nucleophiles comprising one or more of nitrogen,sulfur, or phosphorus as the nucleophilic site.

A fluoroalkene of particular interest for quantifying in or removal fromfluids is PFIB, which, because of its very toxic nature, is notavailable commercially for analytical instrument calibration.2-Perfluorobutene, which is readily available (Lancaster Chemicals Inc.,Lancaster, Pa.), can be chosen as a surrogate of close structureanalogous to PFIB for calibration purposes in the present invention.

In a still further aspect, there is provided a porous, preferablynon-woven, fibrous matrix, preferably a sheet material, comprising animmobilized reactive or sorptive N-, S-, or P-containing nucleophilecoated on high surface area particulate entrapped in the fibrous sheetmaterial, that upon reaction with a fluoroalkene produces anucleophile-fluoroalkene adduct. The high surface area and closeproximity of the entrapped sorptive particles results in rapid reactionkinetics due to the minimal diffusion distances between particles.Porous non-woven fibrous matrices useful in the present invention forimmobilizing nucleophile-coated particles are disclosed, for example, inU.S. Pat. No. 5,635,060, which is incorporated herein by reference.

The present invention provides advantages in removing and quantifyingthe levels of fluoroalkenes in fluids. The quantitative method of thepresent invention permits positive identification of individual highlyfluorinated or perfluorinated alkenes with a thousand-fold increase insensitivity of quantitative measurements compared with existing gaschromatographic methods. In order to avoid contamination of fluidshaving high vapor pressure by generation of a toxic volatile highlyfluorinated or perfluorinated alkene therein, the present inventionprovides a relatively nonvolatile adduct for removing such potentialcontaminants.

The present invention method is also advantageous in that stability ofthe adduct can be selected. In some embodiments, it may be desirable toproduce an unstable adduct so as to decompose or remove highlyfluorinated or perfluorinated alkenes. Hydrous ammonia (ammoniumhydroxide), for example, forms an unstable series of adducts whichrelease HF and appears to completely de-fluorinate PFIB to formtricyanomethane with the release of 8 fluoride ions. This is in contrastto England et al., supra, where anhydrous ammonia, when reacted withhexafluoropropylene dimer, formed a dicyanofluorocarbon,(1-amino-2,2,3,3,3-pentafluoropropylidene)propanedinitrile.

A sorbent can be used to sorb the reaction products. For example,molecular sieves such as Silicalite™, a hydrophobic zeolite (UOP,Tarrytown, N.Y.), can be useful to sorb hydrogen fluoride (HF) and trapother low molecular weight reaction products, both of which can beproduced when highly fluorinated or perfluorinated alkenes react withcertain nucleophiles. In the present invention, Silicalite can act as asubstrate for immobilizing the nucleophiles of the present invention andas a reactant and sorbent for reaction products. It is a preferredsubstrate in that it is not deactivated by water because of its sixAngstrom pore size which prevents water molecule clusters from enteringthe high surface area interior of the particle.

In the present invention heating is not required to activate thenucleophiles. The present invention method takes place at roomtemperature (20-25 degrees C) and no pre-treatment of the nucleophile,as in U.S. Pat. No. 5,462,908, is required.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Highly fluorinated or perfluorinated alkenes that can be removed,immobilized, or quantified according to the method of the inventioninclude alkenes of the formula

wherein A=F or R_(f); X=H, F, Cl, R_(f), or YR_(f); Z=H, F, Cl, orR_(f); and Y=O, N, or S; with the proviso that at least one A=F, and atmost one of Z and X is H; wherein each R_(f) is independently selectedfrom the group consisting of highly fluorinated or perfluorinated alkylgroups; and a combination of any two R_(f) groups can be linked to forma cyclic structure.

The R_(f) alkyl chains may contain from 1-20 carbon atoms, with 1-12carbon atoms preferred. The R_(f) alkyl chains may be straight,branched, or cyclic. Up to twenty heteroatoms or radicals such asdivalent oxygen, trivalent nitrogen or hexavalent sulfur may interruptthe skeletal chain, as is well recognized in the art. When R_(f) is orcontains a cyclic structure, such structure preferably has 5 or 6 ringmembers, 1 or 2 of which can be heteroatoms. “Highly fluorinated” meansthat the degree of fluorination on the chain is sufficient to providethe chain with properties, particularly electronic properties, similarto those of a perfluorinated chain. More particularly, a highlyfluorinated alkyl group will have more than half the total number ofhydrogen atoms replaced with fluorine atoms. Although hydrogen atoms mayremain, it is preferred that at least two hydrogens on each carbonattached to the vinylic carbon atoms be replaced by fluorine, and it ismore preferred that all hydrogen atoms be replaced with fluorine to forma perfluoroalkyl group. It is more preferred that at least two out ofthree hydrogens on the alkyl group be replaced with fluorine, still morepreferred that at least three of four hydrogen atoms be replaced withfluorine and most preferred that all hydrogen atoms be replaced withfluorine to form a perfluorinated alkyl group. Preferably, R_(f) is CF₃,C₂F₅ or C₃F₇.

The ability of highly fluorinated and perfluorinated alkenes to reactwith nuclcophiles is known (see, for example, Zeifman, supra), and isbelieved to be caused by the high electrophilicity of the carbon-carbondouble bond, which, in turn, is believed to be due to the strongelectron withdrawing effects of fluorine atoms and R_(f) groups,particularly CF₃ groups, attached thereto, as well as the capacity ofvinylic fluorine atoms to effectively conjugate with the carbon-carbondouble bond. Of the known fluoroalkenes, perfluoroisobutene (PFIB),having the chemical formula

can be regarded as the most reactive towards nucleophiles, which Zeifman(supra) attributed to the highly electrophilic character of thecarbon-carbon double bond, the lability of the fluorine atoms of the CF₃group, and the possibility of further reactions of any nucleophileaddition products due to the high CH-acidity of, e.g., a(CF₃)₂CH—CF₂-group that may be formed by such an addition reaction.

Nucleophiles capable of reacting with highly fluorinated andperfluorinated alkenes include those comprising a nitrogen-, sulfur- orphosphorus nucleophilic site. Nitrogen-containing nucleophiles useful inthe present invention include ammonia, primary amines, and secondaryamines, preferably secondary amines. Ammonia is known to react with, forexample, PFIB, to yield hexafluoroisobutyronitrile and hydrogen fluoride(Zeifman, supra).

Primary amines useful in the present invention include, in principle,all known primary amines, including aliphatic, aromatic, saturated andunsaturated heterocyclic primary amines. Although primary amines are notthe preferred amine nucleophile of the present invention, liquid primaryamines that can be easily and safely handled under ambient conditions(e.g. 25° C. and one atmosphere pressure), and that readily adsorb orabsorb onto a substrate or carrier, as described below, can be suitablenucleophiles for the present invention. Non-limiting examples of suchprimary amines include propyl amine, n-butyl amine, ethylenediamine,n-octyl amine, aniline, cyclohexylamine, benzylamine, and a myriad ofamines known in the art.

Secondary amines are preferred in the present invention, and, inprinciple, can include all known secondary amines, including aliphatic,aromatic, saturated and unsaturated heterocyclic secondary amines.Secondary amines are preferred in the present invention because they canbe capable of a 1:1 molar reaction with a highly fluorinated orperfluorinated alkene whereby any further reaction of theamine-fluoroalkene adduct with the secondary amine is unlikely, suchthat cleaner, more homogeneous reaction products can be produced.Non-limiting examples of secondary amines useful in the inventioninclude dimethylamine, diethylamine, dibutylamine, dibenzylamine,morpholine, N-methyl aniline, methylbenzylamine, piperidine, pyrrole,pyrrolidine, pyrrolidinone, and piperazine. Preferably, secondary aminesuseful in the present invention include heterocyclic compounds,non-limiting examples of which include morpholine, piperidine, pyrrole,and pyrrolidine. Heterocyclic secondary amines are preferred because oftheir ease of handling and their ready reactivity. Morpholine is themost preferred secondary amine, for purposes of the present invention.

As noted above, the lability of fluorine atoms in the reaction of amineswith fluoroalkenes can generate hydrogen fluoride, HF. Therefore, thereaction can be driven to completion by effective removal of HF. Forthis reason, amines are the preferred nucleophile for the presentinvention, since essentially all known amines exhibit sufficientbasicity to scavenge the HF as it is formed, so that the reaction isdriven to completion. As described in more detail below, the generationand quantification of HF in these reactions provides a useful means ofmeasuring the amount of fluoroalkene in a fluid.

Sulfur-containing nucleophiles useful in the invention comprise thosethat are capable of forming a sulfide anion upon reaction with a base.Examples include thiophenol, benzyl mercaptan, allyl mercaptan, andsalts thereof, such as mercaptides and thiophenoxides. The reaction offluoroalkenes with sulfur nucleophiles can produce either HF or MF,where M is a metal such as sodium, potassium, or the like, that formsthe mercaptide or thiophenoxide salt, and disubstitution to replace bothvinylic fluorine atoms can take place readily.

Phosphorus-containing nucleophiles useful in the invention can includetrialkyl phosphites (e.g., trimethyl phosphite, triethyl phosphite,tri-n-propyl phosphite, tri-n-butyl phosphite), dialkyl phosphines(e.g., di-isopropyl phosphine), and trialkyl phosphines (e.g., trimethylphosphine, triethyl phosphine, tri-n-propyl phosphine, tri-n-butylphosphine).

Particulate supports to which nucleophiles of the invention can bebonded or upon which nucleophiles can be sorbed include those that aresubstantially insoluble in any aqueous or organic fluids comprisingfluoroalkenes that are to be adsorbed, remediated, or quantified bymethods of the invention. “Organic fluids” includes highly fluorinatedor perfluorinated working fluids known in commerce, such asrefrigerants, thermal management fluids, dielectric fluids, and thelike. The particle can be an organic polymer, for example,poly(divinylbenzene), poly(styrene-co-divinylbenzene), or poly- orcopoly-(meth)acrylic acid esters, and derivatives thereof; inorganicoxide particles, for example, silica, alumina, titania, zirconia andother ceramic materials, to which optionally organic groups can bebonded or coated, or which can be coated with aqueous- ororganic-insoluble, non-swellable sorbent material or the surface(internal and/or external) of which can be derivatized to provide acoating of insoluble, non-swellable sorbent material; carbon particles,particularly activated charcoal; molecular sieves, polymer-coated,carbon-clad inorganic oxide particles, such as those described in U.S.Pat. No. 5,271,833, and the like.

Particulate materials useful in the invention can have a diameter offrom about 0.1 to about 600 micrometers, preferably in the range of1-100 micrometers, more preferably in the range of 3 to 100 micrometers.Particle size is chosen so as to maximize available surface area whilealso optimizing fluid flow rate through the particle matrix. Preferablythe surface area is in the range of 50 to 1000 meter²/gram or more.Particulate supports can have a regular shape, for example spherical, oran irregular shape. It has been found advantageous in some instances touse particulate materials in two or more particle size ranges fallingwithin the broad range.

The insoluble, aqueous- or organic-insoluble, non-swellable sorbentcoatings useful in the invention generally have a thickness in the rangeof one molecular layer to about 100 nanometers. Many particles havingcoated surfaces are known, including modified silica particle, forexample, silica particle having bonded thereto organic groups,preferably cyanopropyl, cyclohexyl, phenyl, ethyl, butyl, octyl, andoctadecyl groups. Such coatings preferably readily sorb nucleophiles ofthe invention and are inert toward them.

Sorptive coatings which can be applied to particulate materials can beeither thin mechanical coatings of insoluble, non-swellable polymerssuch as crosslinked silicones, poly(butadienes), etc., or covalentlybonded organic groups such as aliphatic groups of varying chain length(for example, from 2 to 18 carbon atoms).

Molecular sieves useful in the invention, which include zeolites, areinorganic, crystalline materials, usually aluminosilicate compositions,in which the crystal framework of aluminum and silicon atoms forms athree-dimensional network of internal cavities having a honeycomb-likestructure. Many molecular sieves of varying size and constitution arecommercially available.

A particularly useful molecular sieve is Silicalite inorganichydrophobic zeolite commercially available from UOP, Tarrytown, N.Y.,under the trade name Abscents™.

A coconut-based activated charcoal particulate for use in the inventionis preferred.

The particles of the invention can be enmeshed in various porous,fibrous, nonwoven webs or matrices. Types of webs or matrices includefibrillated-polytetrafluoroethylene (PTFE), microfibrous webs,macrofibrous webs, and polymer pulps. Alternatively, in use, particlescan be held in a bed, including a fluidized bed, or packed in a columnor tube. Nucleophilic materials can be coated or sorbed onto particulateprior to or after the particulate becomes enmeshed in a web or is placedin a bed or packed in a column.

Many types of fibrous, nonwoven webs or matrices can be useful in theinvention, including;

1. Fibrillated PTFE

PTFE composite sheet material can be prepared by blending theparticulate or combination of particulates employed with an aqueous PTFEemulsion until a uniform dispersion is obtained and adding a volume ofprocess lubricant up to approximately one half the volume of the blendedparticulate. Blending takes place along with sufficient processlubricant to exceed sorptive capacity of the particles in order togenerate the desired porosity level of the resultant article. Preferredprocess lubricant amounts are in the range of 3 to 200 percent by weightin excess of that required to saturate the particulate, as is disclosedin U.S. Pat. No. 5,071,610. The aqueous PTFE dispersion is then blendedwith the particulate mixture to form a mass having a putty-like ordough-like consistency. The sorptive capacity of the solids of themixture is noted to have been exceeded when small amounts of water canno longer be incorporated into the mass without separation. Thiscondition should be maintained throughout the entire mixing operation.The putty-like mass is then subjected to intensive mixing at atemperature and for a time sufficient to cause initial fibrillation ofthe PTFE particles. Preferably, the temperature of intensive mixing isup to 90° C., preferably it is in the range of 0° to 90° C., morepreferably 20° to 60° C.

Preferably, the weight ratio of particulate to PTFE is in the range of40:1 to 1:40, more preferably 30:1 to 1:30, and most preferably in therange of 20:1 to 1:20.

Mixing times will typically vary from 0.2 to 2 minutes to obtain thenecessary initial fibrillation of the PTFE particles. Initial mixingcauses partial disoriented fibrillation of a substantial portion of thePTFE particles.

Initial fibrillation generally will be noted to be at an optimum within60 seconds after the point when all components have been fullyincorporated into a putty-like (dough-like) consistency.

Devices employed for obtaining the necessary intensive mixing arecommercially available intensive mixing devices which are sometimesreferred to as internal mixers, kneading mixers, double-blade batchmixers as well as intensive mixers and twin screw compounding mixers.The most popular mixer of this type is the sigma-blade or sigma-armmixer. Some commercially available mixers of this type are those soldunder the common designations Banbury mixer, Mogul mixer, C. W.Brabender Prep mixer and C. W. Brabender sigma blade mixer. Othersuitable intensive mixing devices may also be used.

The soft putty-like mass is then transferred to a calendering devicewhere the mass is calendered between gaps in calendering rollspreferably maintained at a temperature up to 125° C., preferably in therange of 0° to about 100° C., more preferably in the range of 20° C. to60° C., to cause additional fibrillation of the PTFE particles of themass, and consolidation while maintaining the water level of the mass atleast at a level of near the sorptive capacity of the solids, untilsufficient fibrillation occurs to produce the desired nonwoven web.Preferably the calendering rolls are made of a rigid material such assteel. A useful calendering device has a pair of rotatable opposedcalendering rolls each of which may be heated and one of which may beadjusted toward the other to reduce the gap or nip between the two.Typically, the gap is adjusted to a setting of 10 millimeters for theinitial pass of the mass and, as calendering operations progress, thegap is reduced until adequate consolidation occurs. At the end of theinitial calendering operation, the resultant sheet is folded and thenrotated 90° to obtain biaxial fibrillation of the PTFE particles.Smaller rotational angles (e.g., 20° to less than 90°) may be preferredin some extraction and chromatographic applications to reduce calenderbiasing, i.e., unidirectional fibrillation and orientation. Excessivecalendering (generally more than two times) reduces the porosity whichin turn reduces the flow-through rate.

During calendering, the lubricant level of the mass is maintained atleast at a level of exceeding the absorptive capacity of the solids byat least 3 percent by weight, until sufficient fibrillation occurs andto produce porosity or void volume of at least 30 percent and preferably40 to 70 percent of total volume. Increased lubricant results inincreased pore size and increased total pore volume as is disclosed inU.S. Pat. No. 5,071,610.

The calendered sheet is then dried under conditions which promote rapiddrying yet will not cause damage to the composite sheet or anyconstituent therein. Preferably drying is carried out at a temperaturebelow 200° C. The preferred means of drying is by use of a forced airoven. The preferred drying temperature range is from 20° C. to about 70°C. The most convenient drying method involves suspending the compositesheet at room temperature for at least 24 hours. The time for drying mayvary depending upon the particular composition, some particulatematerials having a tendency to retain water more than others.

The resultant composite sheet preferably has a tensile strength whenmeasured by a suitable tensile testing device such as an Instron(Canton, Mass.) tensile testing device of at least 0.5 MPa. Theresulting composite sheet has uniform porosity and a void volume of atleast 30 percent of total volume.

The PTFE aqueous dispersion employed in producing the PTFE compositesheet usefull in this invention is a milky-white aqueous suspension ofminute PTFE particles. Typically, the PTFE aqueous dispersion willcontain about 30 percent to about 70 percent by weight solids, the majorportion of such solids being PTFE particles having a particle size inthe range of about 0.05 to about 0.5 micrometers. The commerciallyavailable PTFE aqueous dispersion may contain other ingredients, forexample, surfactant materials and stabilizers which promote continuedsuspension of the PTFE particles.

Such PTFE aqueous dispersions are presently commercially available fromDupont de Nemours Chemical Corp. (Wilmington, Del.), for example, underthe trade names Teflon™ 30, Teflon™ 30B or Teflon™ 42. Teflon™ 30 andTeflon™ 30B contain about 60 percent solids by weight which are for themost part 0.05 to 0.5 micrometer PTFE particles and from about 5.5percent to about 6.5 percent by weight (based on weight of PTFE resin)of non-ionic wetting agent, typically octylphenol polyoxyethylene ornonylphenol polyoxyethylene. Teflon 42 contains about 32 to 35 percentby weight solids and no wetting agent but has a surface layer of organicsolvent to prevent evaporation. A preferred source of PTFE is FLUONM,available from ICI Americas, Inc. Wilmington, Del.

In other embodiments of the present invention, the fibrous membrane(web) can comprise non-woven, macro- or microfibers preferably selectedfrom the group of fibers consisting of polyamide, polyolefin, polyester,polyurethane, glass fiber, polyvinylhalide, or a combination thereof.The fibers preferably are polymeric. (If a combination of polymers isused, a bicomponent fiber may be obtained.) If polyvinylhalide is used,it preferably comprises fluorine of at most 75 percent (by weight) andmore preferably of at most 65 percent (by weight). Addition of asurfactant to such webs may be desirable to increase the wettability ofthe component fibers.

2. Macrofibers

The web can comprise thermoplastic, melt-extruded, large-diameter fiberswhich have been mechanically-calendered, air-laid, or spunbonded. Thesefibers have average diameters in the general range of 50 μm to 1,000 μm.

Such non-woven webs with large-diameter fibers can be prepared by aspunbond process which is well known in the art. (See, e.g., U.S. Pat.Nos. 3,338,992, 3,509,009, and 3,528,129.) As described in thesereferences, a post-fiber spinning web-consolidation step (i.e.,calendering) is required to produce a self-supporting web. Spunbondedwebs are commercially available from, for example, AMOCO, Inc.(Napierville, Ill.).

Non-woven webs made from large-diameter staple fibers can also be formedon carding or air-laid machines (such as a Rando-Webber™ Model 12BS madeby Curlator Corp., East Rochester, N.Y.), as is well known in the art.See, e.g., U.S. Pat. Nos. 4,437,271, 4,893,439, 5,030,496, and5,082,720.

A binder is normally used to produce self-supporting webs prepared bythe air-laying and carding processes and is optional where the spunbondprocess is used. Such binders can take the form of resin systems whichare applied after web formation or of binder fibers which areincorporated into the web during the air laying process.

Examples of common binder fibers include adhesive-only type fibers suchas Kodel™ 43UD (Eastman Chemical Products, Kingsport, Tenn.) andbicomponent fibers, which are available in either side-by-side form(e.g., Chisso ES Fibers, Chisso Corp., Osaka, Japan) or sheath-core form(e.g., Melty™ Fiber Type 4080, Unitika Ltd., Osaka, Japan). Applicationof heat and/or radiation to the web “cures” either type of binder systemand consolidates the web.

Generally speaking, non-woven webs comprising macrofibers haverelatively large voids. Therefore, such webs have low capture efficiencyof small-diameter particulate (reactive supports) which is introducedinto the web. Nevertheless, particulate can be incorporated into thenon-woven webs by at least four means. First, where relatively largeparticulate is to be used, it can be added directly to the web, which isthen calendered to actually enmesh the particulate in the web (much likethe PTFE webs described previously). Second, particulate can beincorporated into the primary binder system (discussed above) which isapplied to the non-woven web. Curing of this binder adhesively attachesthe particulate to the web. Third, a secondary binder system can beintroduced into the web. Once the particulate is added to the web, thesecondary binder is cured (independent of the primary system) toadhesively incorporate the particulate into the web. Fourth, where abinder fiber has been introduced into the web during the air laying orcarding process, such a fiber can be heated above its softeningtemperature. This adhesively captures particulate which is introducedinto the web. Of these methods involving non-PTFE macrofibers, thoseusing a binder system are generally the most effective in capturingparticulate. Adhesive levels which will promote point contact adhesionare preferred.

Once the particles have been added, the loaded webs are typicallyfurther consolidated by, for example, a calendering process. Thisfurther enmeshes the particles within the web structure.

Webs comprising larger diameter fibers (i.e., fibers which averagediameters between 50 μm and 1,000 μm) have relatively high flow ratesbecause they have a relatively large mean void size.

3. Microfibers

When the fibrous web comprises non-woven microfibers, those microfibersprovide thermoplastic, melt-blown polymeric materials having activeparticles dispersed therein. Preferred polymeric materials include suchpolyolefins as polypropylene and polyethylene, preferably furthercomprising a surfactant, as described in, for example, U.S. Pat. No.4,933,229. Alternatively, surfactant can be applied to a blownmicrofibrous (BMF) web subsequent to web formation. Polyamide can alsobe used. Particulate can be incorporated into BMF webs as described inU.S. Pat. No. 3,971,373.

Microfibrous webs of the present invention have average fiber diametersup to 50 μm, preferably from 2 μm to 25 μm, and most preferably from 3μm to 10 μm. Because the void sizes in such webs range from 0.1 μm to 10μm, preferably from 0.5 μm to 5 μm, flow through these webs is not asgreat as is flow through the macrofibrous webs described above.

4. Cast Porous Membranes

Solution-cast porous membranes can be provided by methods known in theart. Such polymeric porous membranes can be, for example, polyolefinincluding polypropylene, polyamide, polyester, polyvinyl chloride, andpolyvinyl acetate fibers.

5. Fibrous Pulps

The present invention also provides the use of a sheet materialcomprising a porous fibrous pulp, preferably a polymeric pulp,comprising a plurality of fibers that mechanically entrap activeparticles, and preferably the sheet also comprises a polymerichydrocarbon binder, the weight ratio of particles to binder being atleast 13:1 and the ratio of average uncalendered sheet thickness toeffective average particle diameter being at least 125:1.

Generally, the fibers that make up the porous polymeric pulp of thesheet material useful in the present invention can be any pulpable fiber(i.e., any fiber that can be made into a porous pulp). Preferred fibersare those that are stable to radiation and/or to a wide range of pH (1through 14). Examples include polyamide fibers and those polyolefinfibers that can be formed into a pulp including, but not limited to,polyethylene and polypropylene. Particularly preferred fibers arearomatic polyamide fibers and aramid fibers because of their stabilityto both radiation and highly caustic fluids. Examples of useful aromaticpolyamide fibers are those fibers of the nylon family. Polyacrylicnitrile, cellulose, and glass can also be used. Combinations of pulpscan be used.

Examples of useful aramid fibers are those fibers sold under the tradename Kevlar™ (DuPont, Wilmington, Del.). Kevlar fiber pulps arecommercially available in three grades based on the length of the fibersthat make up the pulp. Regardless of the type of fiber(s) chosen to makeup the pulp, the relative amount of fiber in the resulting sheet (whendried) ranges from about 12.5 percent to about 30 percent (by weight),preferably from about 15 percent to 25 percent (by weight).

Useful binders for sheets useful in the present invention are thosematerials that are stable over a range of pH (especially high pH) andthat exhibit little or no interaction (i.e., chemical reaction) with anyof the fibers of the pulp, the particles entrapped therein, orfluoroalkenes. Polymeric hydrocarbon materials, originally in the formof latexes, have been found to be especially useful. Common examples ofuseful binders include, but are not limited to, natural rubbers,neoprene, styrene-butadiene copolymer, acrylate resins, and polyvinylacetate. Preferred binders include neoprene and styrene-butadienecopolymer. Regardless of the type of binder used, the relative amount ofbinder in the resulting sheet (when dried) is about 3 percent to about 7percent, preferably about 5 percent. The preferred amount has been foundto provide sheets with nearly the same physical integrity a sheets thatinclude about 7 percent binder while allowing for as great a particleloading as possible. It may be desirable to add a surfactant to thefibrous pulp, preferably in small amounts up to about 0.25 weightpercent of the composite.

Because the capacity and efficiency of the sheet depends on the amountof particles included therein, high particle loading is desirable. Therelative amount of particles in a given sheet material useful in thepresent invention is preferably at least about 65 percent (by weight),more preferably at least about 70 percent (by weight), and mostpreferably at least about 75 percent (by weight). Additionally, theweight percentage of particles in the resulting sheet is at least 13times greater than the weight percentage of binder, preferably at least14 times greater than the weight percentage of binder, more preferablyat least 15 times greater than the weight percentage of binder.

Regardless of the type or amount of the particles used in the sheetmaterial useful in the present invention, they are mechanicallyentrapped or entangled in the fibers of the porous pulp. In other words,the particles are not covalently bonded to the fibers.

The method of reacting a nucleophile, particularly an amine or anitrogen-containing nucleophile, with a fluoroalkene as described hereinfinds utility in absorbing and removing the fluoroalkenes from fluids inwhich they may be present. In the invention, “removal” includes chemicalreactions that destroy or sufficiently change or reduce the volatilityor toxicity of fluoroalkenes. Such chemical reactions may liberatehydrogen fluoride (HF), such that determination of the amount of HFliberated provides an indirect measure of the amount of fluoroalkene inthe fluid. Thus, the method of the invention is useful for remediationof highly fluorinated or perfluorinated working fluids, includingindustrial reaction and waste streams, to remove potentially toxic ordangerous fluoroalkenes, the most notable of which is PFIB. In addition,the method of the invention provides a convenient, direct method forquantification of certain fluoroalkenes due to precise identification offluoroalkene-nucleophile adduct(s) by, for example, GC/MS methods.Finally, the method of the invention provides a means of continuouscleaning of highly fluorinated and perfluorinated working fluids bycirculating them through a bed or column or particle-loaded fibrous webcomprising support particles to which or on which nucleophiles aresorbed or coated.

In a preferred embodiment of the invention, an amine, preferably asecondary amine, and more preferably morpholine, was adsorbed ontosilica gel particles that previously had been packed into a tube. Afixed amount of fluid containing a fluoroalkene was passed through thetube, and the effluent was analyzed by GC/MS for the presence of thefluoroalkene to determine the capacity of the tube.

Alternatively, particles, such as activated charcoal, can be enmeshed ina fibrillated PTFE web, such as are commercially available as Empore™nonwoven webs, from 3M, St. Paul, Minn. Preferably, the activatedcharcoal particles are coated with morpholine by soaking theparticle-loaded Empore™ web in morpholine solution, then air-drying theweb to remove residual solvent. Then the fluid containing a fluoroalkeneto be quantified or removed is passed through the morpholine treated webwhich is placed in a standard solid phase extraction (SPE) web holder.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

Perfluorinated liquids can be used as coolants for electronic devices(e.g., supercomputers) and as heat transfer media in vapor-phasesoldering processes. Toxic fluoroalkene impurities can form upontransient heating of perfluorinated liquids which are used in manyindustrial processes. The methods and materials of the present inventionare environmentally advantageous because (1) they can be used to removefluoroalkenes, including PFIB, from fluids frequently used in industryand (2) they teach methods to detect and monitor the presence of thesereactive fluoroalkenes at low levels.

EXAMPLES

All materials not otherwise identified in the examples were purchasedfrom Aldrich Chemical Co., Milwaukee, Wis.

Example 1 Reactions of PFIB with Ammonium Hydroxide to Form UnstableAdducts

A gas standard containing 10 μL PFIB (Fluorochem, Ltd. Derbyshire, UK)per mL of air was prepared in a glass sampling bulb. One hundred μL ofthis gas standard was mixed with 40 mL of perfluorohexane (FC_(72,)commercially available from 3M Inert Fluids Group, St. Paul, Minn.) togive a nominal concentration of 25 nL gaseous PFIB per mL solution.Eight mL aliquots of this standard solution were vortexed (shakenvigorously) for seven minutes in 14 mL volume polystyrene centrifugetubes (Falcon™ brand, #2001, VWR Scientific Products, South Plainfield,N.J.) together with 0.2 mL of concentrated (34 wt %) ammonium hydroxide.After this, each sample was treated with 2 mL of a special total ionicstrength adjusting buffer (TISAB-B, nominal 4 molar aceticacid/potassium acetate buffer at pH=5.0, described in Orion Fluoride ionselective electrode (ISE) manuals, Orion Corp. Beverly, Mass.). Thesamples were vortexed again, after which phase separation took place. AnOrion combination Fluoride ISE in combination with an Orion 920 ISEmeter was used to measure fluoride concentration of the aqueous phase inthe sample tube. Control samples of perfluorohexane without PFIB werecarried through the entire process, as was a TISAB-B/ammonia blank,neither of which reacted. PFIB in the solution of perfluorohexane whenmixed with hydrous ammonia (ammonium hydroxide) formed an unstableaddition product, which spontaneously eliminated HF forming a secondfluoroalkene species. This was followed by sequential addition reactionsof ammonia with the alkenes produced by the elimination of HF, to formsecondary adducts and subsequent elimination reactions of HF from theadducts until the starting PFIB was highly defluorinated. Fluoride ionconcentration observed was proportional to PFIB added to the solutions,and recovery of fluoride ion from PFIB was eighty percent of theoreticaltotal fluorine. These proposed reactions are shown in Reaction Sequence1 below.

As a comparative, 1H-pentadecafluoroheptane (a representativehydrofluoroalkane) was evaluated in the liquid solution mode forreactivity with ammonia/ammonium hydroxide. There was no measurablereaction at room temperature when vortexed for ten minutes in the samemanner as described for the PFIB liquid solution samples under theconditions previously described.

The data from this Example show that these reaction conditions removednearly all the S fluorine from PFIB but did not dehydrofluorinatehydrofluoroalkanes containing CF₂H-group to form fluoride ions.

Example 2 PFIB Adduct Formation with Ammonium Hydroxide on SolidSupports

A vapor phase assay was developed using ammonium hydroxide sorbed onsolid supports packed in glass sampling tubes. The tube types were: 1)Acid-mist silica tubes (cat. #226-10-03), 2) Silica tubes (cat.#226-15), and 3) Charcoal tubes (cat. #226-09), all from SKC Inc.,Fullerton, Calif. The tubes were evaluated both as received (untreated)and by loading each of them with 200 μL of concentrated ammoniumhydroxide (treated) and subsequently sealing them with plastic capsuntil they were evaluated.

A gas standard containing 10 nL PFIB (Fluorochem, cited above) per mL ofair (10 ppm PFIB) was prepared in a glass sampling bulb. Portions ofthis standard accurately diluted in air or in nitrogen were passedthrough these tubes to determine capture efficiency. Each of the tubeswas exposed to one liter of 1 ppm PFIB gas in air followed by about 9liters of ambient air (as flush for the source bulb). GC analysis ofPFIB in the gaseous effluent from the tubes showed the two types of SKCsilica tubes, untreated and treated with ammonium hydroxide, did notremove PFIB effectively (about 50 percent recovery) while untreated andtreated charcoal tubes did remove PFIB effectively.

Each of the charcoal tubes were eluted with three 200 μL aliquots ofconcentrated ammonium hydroxide and then with 1 mL deionized water andfinally with 5 mL of TISAB-B solution. Fluoride ion levels weredetermined with the ISE as described in Example 1. Recovery of PFIB asindicated by measurement of fluoride ion from treated charcoal tubes was75 percent of the theoretical fluoride; tubes not pretreated gave PFIBrecoveries of 50 percent as determined by the measurement of fluorideion.

The results of this Example show that PFIB reacted efficiently withammonium hydroxide when immobilized on a high surface area solidsupport.

Example 3 Quantitative Determination of PFIB

Four SKC charcoal sampling tubes were each pretreated with 200 μLammonium hydroxide as described Example in 2. Each of the tubes wasexposed to one liter of 1 ppm PFIB gas in air followed by approximately9 liters of ambient air (as flush for the source bulb). The charcoaltubes were processed in steps: 1) the tubes were opened andseparated—the front section of charcoal and the backup section pouredinto individual polystyrene (PS) culture tubes; 2) 200 μL ofconcentrated ammonium hydroxide were added to the charcoal in each PStube and the poly cap was applied (total of eight tubes). The tubes wereshaken and allowed to equilibrate for five minutes; 3) 2 mL of 4 molarTISAB-B was added to each tube, the cap was re-sealed, and the tubeswere shaken; 4) Fluoride concentration was measured for each tube usingthe ISE as described in Example 1.

The advantage of gas sampling is that a large volume of gas may be sweptthrough a small cartridge to effect concentration of the analyte ofinterest, PFIB in this case. In a second trial to further evaluatedynamic gas phase analysis, an apparatus was constructed to deliver aknown concentration and flow rate of PFIB in a large volume of air ornitrogen. For each sample a microprocessor controlled syringe drive(from Hamilton Co., Reno, Nev.) with a polypropylene 50 cc syringe wasused to deliver a constant flow of a relatively concentrated (between300 and 10,000 μL PFIB per L air) PFIB-air mixture into a mixing tee. Anair stream was delivered into the mixing tee via a line with anover-pressure by-pass, and the total flow through the tee past the PFIBdelivery port was controlled by a calibrated Industrial Hygiene samplingpump (Industrial Hygiene Specialties, Columbus, Ohio). After passingthrough a short length of polyethylene tubing the dilute PFIB/nitrogensolution was directed through a pre-treated (as described in Example 2)ammonium hydroxide-on-charcoal sorbent tube. Sample tubes were processedas described in Example 2, and recovery of fluoride ion derived fromPFIB was quantitative.

The data of Table 1 below show that the efficiency of large volumesampling approached 100 percent for quantitative determination of PFIBconcentrations between 3.4 ppb and 100 ppb in a gas sample. At 10,000ppb the capacity of this system was exceeded such that not all of thefluorine was recovered as fluoride.

TABLE 1 Large Volume Sampling* for Low Level PFIB by Sorption andMeasurement of Fluoride Fluoride Replicate Sweep Volume PFIBconcentration % Recovery Precision 10 liters 10,000 ppb  69% +/− 1% 10liters 10,000 ppb  61% +/− 0% 10 liters 100 ppb 113% +/− 6% 10 liters100 ppb 101% +/− 6% 50 liters 55.1 ppb 112% +/− 3% 50 liters 8.0 ppb109% +/− 5% 50 liters 3.4 ppb  99% +/− 5% *Sampled at a rate of 1 literper minute for 10 liters and at a rate of 5 liters per minute for 50liters

Perfluoropropene (hexafluoropropene, HFP) was evaluated for itsreactivity in the gas phase capture mode. It reacted with ammoniumhydroxide, and was apparently less reactive than PFIB, since HFP wastrapped at only 70 percent efficiency as determined by release offluoride ion.

The quantitative defluorination of PFIB was developed into a simplefield method for measurement of PFIB via measurement of the fluoride ionlevels. This Example showed that defluorination of PFIB could beperformed in a quantitative, exhaustive and reproducible manner to givea useful analytical method for the indirect measurement of PFIB at ppbconcentrations in a fluid medium.

Example 4 Reactions of PFIB with Cyclic Amine Nucleophiles to FormStable Adducts

Amine compounds were evaluated for their ability to form PFIB adducts.Morpholine-fluoroalkene adducts were preferred when stable adducts offluoroalkene mixtures were desired for analytical or separationpurposes. This Example showed that the addition of secondary aminenucleophiles to PFIB with the subsequent elimination of HF can formstable adducts. Production of the adducts were confirmed by the GC/MSmethod of Example. 5 below. Equation 1 illustrates the specific exampleof morpholine reacting with PFIB.

C₄H₈ONH+CF₂=C(CF₃)₂→C₄H₈ONCF=C(CF₃)₂+HF  1

The mass spectrum of the PFIB-morpholine adduct showed a base peak ofm/z 223 and other significant peaks at m/z 267, m/z 248, m/z 209, m/z208, and m/z 69. The expected molecular ion of the adduct at m/z 287 wasnot observed in the spectrum. It was postulated that the PFIB-morpholineadduct lost HF in solution prior to injection for GC/MS analysis. Thishypothesis was supported by chemical ionization mass spectrometryanalyses of the PFIB-morpholine standards using both methane andisobutane as the reagent gases. These analyses showed only twosignificant ion masses, one at m/z 268 which corresponded to theprotonated molecular ion and one at m/z 248 which appeared to resultfrom the loss of HF from the protonated molecular ion. Suggestedfragmentation/rearrangement pathways are summarized in Reaction Sequence2, below. The m/z 223 ion may represent a unique ion mass characteristicof PFIB adducts produced by reaction with cyclic secondary amines. Thision mass was also observed in the mass spectra of the adducts producedby reaction of PFIB with pyrrolidine and piperidine.

The m/z 248 ion resulted from the loss of F from the m/z 267, while theorigin of the m/z 209 and m/z 208 ion mass were less obvious. The m/z208 ion mass is believed to have resulted from the loss of CH₃. from them/z 223 ion and the m/z 209 ion mass from the loss of CH₃. from the m/z224 ion.

Example 5 Reaction of Fluoroalkenes with Nucleophile-coated Substrates

Various substrates were evaluated for their ability to removefluoroalkenes. The substrates included high surface area activatedsilica gel (Aldrich Chemical Company, Milwaukee, Wis.) and Silicalite™molecular sieves as well as these substrates coated with nucleophiles.The fluoroalkene removal efficiencies were determined fordeactivated-silica gel, activated-silica gel, and with nucleophilesimmobilized on silica gel. Evaluations were carried out by passingfluoroalkenes through 4 mm internal diameter glass tubes that wereapproximately 75 mm long and packed with coated or uncoated sorbents.The fluoroalkenes were passed through the tubes using 20 mL or 50 mLglass syringes. One syringe contained the fluoroalkene (1,000 ppm inair) used to challenge the silica gel, while the other was used tocollect the gas that had passed through the tube. The fluoroalkene waspassed through the silica gel tubes at approximately 1 mL per second.The fluoroalkenes that were evaluated included perfluoro-2-butene and2H-pentafluoropropene.

Both perfluoro-2-butene and 2-hydro-pentafluoropropene were completelyretained on activated silica gel. When the silica gel was deactivated byambient moisture, or by the addition of 5% by weight water, neitherfluoroalkene was retained. In addition, 2-hydro-pentafluoropropene wasnot desorbed from the activated silica gel using methyl-t-butyl ether(MTBE) elution solvent. However, when the MTBE elution solvent contained5% by volume of morpholine, the 2-hydro-pentafluoropropene wasquantitatively desorbed initially as the unreacted fluoroalkene.Subsequent re-analyses (next day) of the eluting solvent showed that the2-hydro-pentafluoropropene had reacted with morpholine in the solutionto form the 2-hydro-pentafluoropropene-morpholine adduct with subsequentspontaneous elimination of HF.

Both perfluoro-2-butene and 2-hydro-pentafluoropropene were retained onsilica gel coated with approximately 10 weight percent morpholine basedupon the weight of silica gel. Approximately 98% of theperfluoro-2-butene was retained, while 100% of the2-hydro-pentafluoropropene was retained. When the silica gel was coatedwith piperazine, only 28% of the perfluoro-2-butene was retained.Similar trials using Silicalite coated with 5% morpholine orN-methylethylenediamine showed that 99-100% of the perfluoro-2-butenewas retained. Silicalite™ was the preferred absorbent substrate since itwas not de-activated by water.

Table 2 lists molecular ions and base peak ions observed in the MSanalyses of a series of fluorinated alkene adducts with morpholine. Thistable also summarizes the relative reaction rates of fluoroalkenes withmorpholine.

TABLE 2 Morpholine-Perfluoroolefin Adducts Speed of Molecular Ion BasePeak Fluorocarbon Reaction* (m/z) (m/z) 1-perfluoropropene Fast 237 1362-hydropentafluoropropene Fast 199 199 2-perfluorobutene Slow 267 267Perfluorocyclobutene Intermediate 229 229 1-perfluoropentene Fast 317317 1,3-hexafluorobutadiene Fast 229 229 perfluoroisobutene Fast 267 223perfluoroethylene Intermediate 187 136 perfluoro-3-methyl-1-butene Fast337/317 136/248 octafluorocyclopentene Fast 279 2791,1-dihydrodifluoroethylene No Rx — — *FAST means reaction is completein 30 minutes or less INTERMEDIATE means between 30 minutes and 3 hoursSLOW means greater than 3 hours

1,2-dihydrotetrafluoroethane and 1,2-dihydrohexafluoropropane did notreact with morpholine in comparison to the fluoroalkene species, thusallowing the adduct formation to be useful in removing or quantifyingfluororalkenes in bulk quantities of these fluoroalkane fluids.

Example 6 Specificity of N-methylaniline for PFIB Nucleophile—AdductFormation

The amines listed in Table 3, below, were evaluated for reactivity withPFIB using the following procedure: The samples were prepared in glassautosampler vials having Teflon™ lined-rubber septum crimp caps (KimbleGlass, Vineland, N.J.). Portions of each of the amines were diluted withmethyl t-butyl ether (MTBE) to produce 10% (v/v) solutions. Aziridinewas purchased from Columbia Organic Chemicals, Columbia, S.C. A 1 mLvolume of each amine solution was transferred to separate vials whichwere then capped. A 1 mL volume of a 10,000 ppm (v/v) standard ofperfluoroisobutene (PFIB) in air was then introduced into the headspaceof each vial using a gas-tight syringe. The vials were gently shaken forseveral minutes, then placed into the autosampler tray of thechromatograph for analysis. Analyses were obtained using GC/MS asdescribed in Example 4. N-methylaniline was highly selective, forming anadduct with PFIB exclusively, under the test conditions described.

TABLE 3 Nucleophiles Reacted with PFIB Nucleophile Product AmmoniaTricyanomethane + HF Aziridine Adduct − HF Benzenethiol (Thiophenol) ″Benzylamine No Reaction under conditions employed Dibenzylamine ″Methylamine Adduct − HF Propylamine ″ Dimethylamine ″ Diethylamine ″Dipropylamine ″ Dibutylamine ″ Dicyclohexylamine ″ Ethylenediamine NoReaction under conditions employed 2-Methoxyethylamine ″ MorpholineAdduct − HF N-Methylaniline ″ Methylbenzylamine ″ Piperidine ″ Pyrrole ″pyrrolidine ″ Pyrrolidinone Adduct Piperazine Adduct − 2HFs

Example 7 Reactions of Fluoroalkene-nucleophile Adducts to FormSecondary Reaction Products

The fluoroalkene-nucleophile adduct solutions of Example 6, comprisingolefinic amine adducts resulting from the spontaneous elimination of HF,were treated with water or methanol to provide a 2 percent volume/volumesolution. A secondary reaction involving addition of water or alcohol tothe fluoroalkene-amine adduct was observed by the GCIMS analysis methoddescribed in Example 4.

The GC/MS data indicated that the initial water or methanol adducts alsounderwent further elimination reactions to form an amide (from water)and a vinyl ether (from methanol). The amide and vinyl ether thus formedwere considered to be more stable than a) the initial adduct before thefirst HF elimination, b) the resultant olefinic amine adduct, and c) thewater and alcohol addition product adducts. This series of reactions forthe morpholine adduct of PFIB is illustrated in Reaction Sequence 3. Thefinal amide (V) and vinyl ether (VII) were not as readily susceptible tofurther addition or hydrolysis reactions.

Example 8 Identification and Quantification of Fluoroalkenes

Instrument calibration standards were prepared by passing a known volumeof air spiked with a known volume of PFIB through a tube packed withmorpholine-treated silica gel at a maximum rate of 0.5 L/min. ThePFIB-morpholine adduct was then eluted from the tube with methyltert-butyl ether (MTBE) and the resulting solution serially diluted toproduce the standard calibration solutions. The lowest concentrationstandard was 13 parts-per-billion (ppb). The calibration curves preparedfrom both the fill scan and selective ion monitoring (SIM) analyses werelinear over several orders of magnitude. In principle, the lowercalibration limit may be extended from 13 ppb down to at least 100parts-per-trillion (ppt) using SIM data acquisition. Generation ofstandards in this manner would compensate for incomplete reaction toform the adduct or incomplete recovery of the adduct from the silicagel, assuming an unknown sample was treated similarly to the standards.

Standard solutions and sample extracts were analyzed using combinedcapillary column gas chromatography/low resolution mass spectrometry(GC/MS). The initial analyses were carried out using full scan massspectrometry. The later analyses were carried out using (SIM) massspectrometry which provided better sensitivity. Standard solutions andsample extracts were analyzed using a Hewlett Packard Model 5970 MassSelective Detector (MSD) interfaced to a Hewlett Packard Model 5890 GasChromatograph (Hewlett Packard Co., Instruments Division, Palo Alto,Calif.). The mass spectrometer was scanned between 35-350 amu for thefull scan analyses and selectively jumped between m/z 223 and m/z 267for the SIM analyses. Electron impact ionization (EI) at a nominal 70 eVwas used. Components in the MTBE solutions were separated using a 30meter DB-5 capillary column having an internal diameter of 0.25 mm and afilm thickness of 1 um. The gas chromatograph was operated with aconstant column head pressure of 69 kPa and a temperature program of 10°C./minute from 40° C. to 300° C. The column temperature was held at theinitial temperature for one minute before programming and the injectortemperature was maintained at 250° C. Using these conditions, thePFIB-morpholine adduct was completely separated from the solvent, theexcess morpholine, and from other compounds present in the extracts. Ofthe two ion masses monitored for the SIM analyses, the m/z 223 ion wasthe most unique and exhibited the least response to other compoundspresent in the extract.

Example 9 Reaction of PFIB with a Sulfur Containing Nucleophile

Thiophenol was reacted with PFIB using the procedure described inExample 6. A stable adduct was formed which could be isolated andidentified by GC/MS. Molecular ions with m/z of 310 and 290 weredetected which indicated that both the original thiophenol-PFIB adductand the adduct after elimination of HF were present. Reaction Sequence 4below, illustrates the reaction and proposed mass spectrometric ion massassignment fragmentation patterns observed.

Example 10 Reaction of PFIB with a Phosphorous Nucleophile

Trimethylphosphite (TMP) reagent was prepared by adding 22.5 microlitersof TMP to 1.5 mL of acetonitrile in a sealed autosampler vial. Apolypropylene syringe was used to add 1.0 mL of this reagent to each ofthe vials containing 15 mL of a) standards of PFIB in perfluorohexaneand b) test samples. The sample vial was placed on a shaker at highspeed for three hours, the acetonitrile layer was transferred to anautosampler vial, and the sample was immediately analyzed by GC.Chromatographic conditions were: HP5890 gas chromatograph with ElectronCapture detector and HP7673A autosampler (Hewlett Packard, Palo Alto,Calif.); 30 meter DB-210 column with 0.32 mm internal diameter and 0.5μm film thickness; Nitrogen carrier/makeup gas; Oven program 60° C.initial to 160° C. final programmed at 5 deg. per minute for a 20 minuterun; Injection port 120° C.; Detector temperature 240° C.; Splitlessinjection with 1 microliter sample size.

Reaction Sequence 5 illustrates the proposed reaction products.Structure VIII was the major adduct, confirmed by mass spectrometry. Itis believed that trimethyl phosphite is specific for PFIB and does notform adducts with other less reactive fluoroalkenes.

Three product peaks were generated in the chromatograms, consistent withthree products from this reaction. The first product (VII) was convertedto the other two. The earliest eluting chromatographic peak was used forcalibration and quantitation. Detection limit was established as tenparts per billion (ppb). Table 4 gives recovery data for this method.

TABLE 4 Recovery of PEIB by Different GC Methods and in Different FluidsPFIB Found (ppb) TMP PFIB Direct GC Derivatization Fluid Expected (ppb)Carbopack B DB 210 Perfluorooctane 50 43 ± 6.2 52 ± 3.6 (n = 5) (n = 5)Perfluoro- 20 analysis not possible 18 ± 3.2 hexane (n = 5)

Example 11 PFIB-morpholine Adduct Formation Using Particle LoadedMembranes

Porous particle loaded membrane disks of four types were tested fortheir ability to remove PFIB from a gaseous stream and to form thePFIB-morpholine adduct in-situ. The membranes used were 3M PTFE matrixEmpore™ membranes containing 1) octadecylsilane bonded silica, 2)styrene-divinylbenzene resin, 3) carbon, (all available from FisherScientific, Pittsburgh, Pa.) and 4) Silicalite™ enmeshed in apolypropylene matrix (from 3M Co. St. Paul, Minn. as described in U.S.Pat. No. 5,529,686, Example 3). The disks were approximately 0.5 mmthick and 25 mm in diameter. They were held in a stainless steel filterholder (Millipore Corp., Bedford, Mass.). They were tested for theirability to sorb PFIB as 1) received (or un-treated) and 2) treated withmorpholine. The treated disks were prepared by soaking the disks in a 10volume % solution of morpholine in methyl tert-butyl ether solvent. Theywere removed from the solution and allowed to air dry for 24 hours toremove the volatiles.

One hundred mL gas sampling bulbs containing 1000 ppm by vol PFIB in airwere prepared as described in Example 1. The 100 mL bulb was connectedto membrane holder in series with a 1.27 cm long 26 gauge hypodermicneedle acting as a flow restrictor. The flow restrictor was connected toan evacuated 1000 mL gas sampling bulb which was used to draw thecontents of the 100 mL sample bulb through the membrane being tested.The flow rate was measured and found to be 0.2 liters per minute.

PFIB levels in the 1000 mL bulb acting as a receiver for the contents of100 mL sample bulb were analyzed by GC as described in Example 2. Of theuntreated membrane disks tested, only the carbon disk membrane waseffective in removing the PFIB, as evidenced by the absence of PFIB inthe receiver bulb. The other untreated disks were not effective inretaining PFIB by sorption. When coated with morpholine, all of thedisks were effective at removing PFIB by sorption or reaction, asevidenced by the absence of PFIB in the receiver bulbs.

A Silicalite loaded membrane disk (treated with morpholine and exposedto PFIB as described above) was removed from its holder and extractedwith MTBE to establish the proposed PFIB morpholine adduct formationunder these conditions. The extract was analyzed by GC/MS as describedin Example 8 and was found to contain the adduct showing that thereaction with PFIB was rapid under these conditions. Small amounts ofhexafluoropropylene, perfluoro-1-butene, and perfluoro-2-butene werepresent in the PFIB gas standard and these were not retained by, nor didthey form adducts with, the morpholine coated disks under the conditionsof this example. The rates of reaction of PFIB with nucleophiles areknown to be faster than with other fluoroalkenes and these conditionswere insufficient for the fluoroalkenes with slower reaction rates.Slower flow rates, thicker disks (longer pathlengths), and largerdiameter disks can be used to increase the residence times of thoseanalytes in the disk to allow for optimum reaction conditions.

This example showed that nucleophile-coated, high surface areaparticles, entrapped in porous fibril matrices can effectively serve asreaction media for removing PFIB from fluids.

The data of the examples of the present invention clearly show that theformation of fluoroolefin-N, -S, or -P nucleophile adducts provided ameans of converting, removing, identifying, and quantifyingfluoroolefins such as PFIB in fluids. The ability to form unstableadducts as with ammonium hydroxide provided a method for destruction oftoxic fluoroolefins, such as PFIB, for remedial purposes. The formationof stable adducts provided a means for immobilizing and for positivelyidentifying and quantifying fluoroolefins in fluids such as gas andliquids. The use of organic nucleophiles to convert volatile and/ortoxic fluoroolefins to a relatively less toxic and lower volatilityspecies is of great utility. Fluoroolefin products, obtained by HFeliminations from primary fluoroalkene-nucleophile adducts, werethemselves capable of further reactions with nucleophiles such as waterand alcohols to form stable and useful products such as fluorinatedamides and vinyl ethers when N-nucleophiles were used.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand intent of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodiment setforth herein.

We claim:
 1. A method for removing perfluoroisobutene from a fluidcomprising the step of contacting the fluid with N-methylaniline for atime sufficient to form an N-methylaniline-perfluoroisobutene adduct. 2.The method according to claim 1 wherein saidN-methylaniline-perfluoroisobutene adduct is bonded or sorbed to asupport.
 3. The method according to claim 2 wherein said support isselected from the group consisting of (a) organic polymeric supportswhich optionally can be clad with a sorptive coating; (b) inorganicparticulate supports which optionally can be clad with a sorptivecoating; and (c) carbon particulates.
 4. The method according to claim 2wherein said support is a particulate support.
 5. The method accordingto claim 4 wherein said particulate support is a molecular sieve.
 6. Themethod according to claim 4 wherein said particulate support is enmeshedin a porous, fibrous web.
 7. The method according to claim 6 whereinsaid porous, fibrous web is selected from the group consisting offibrillated polytetrafluoroethylene, microfibrous webs, macrofibrouswebs, and polymer pulps.
 8. The method according to claim 4 wherein saidparticulate support is in a bed, column, or tube.
 9. A method forquantifying perfluoroisobutene in a fluid comprising the steps of: a)providing an N-methylaniline-perfluoroisobutene adduct, said adductbeing sorbed or bonded to a support, and b) displacing said adduct fromsaid support for indirect quantification of perfluoroisobutene.
 10. Amethod for quantifying perfluoroisobutene in a fluid comprising thesteps of: a) providing an N-methylaniline-perfluoroisobutene adduct,said adduct being sorbed or bonded to a support, and b) measuringfluoride ion for indirect quantification of perfluoroisobutene.
 11. Amethod for isolating perfluoroisobutene from a fluid comprising two ormore fluoroalkenes comprising the step of contacting the fluid withN-methylaniline for a time sufficient to form anN-methylaniline-perfluoroisobutene adduct.